Preparation Of Graphene-based Composites And Their Electrochemical Sensing Of Drugs

Graphene has drawn considerable attention due to its super properties such as fast electron transfer,perfect quantum tunnel effect and large surface area.However,due to the inevitable aggregation between individual graphene sheets driven by strong van der Waals'force,graphene tends to easily form irreversible agglomerates,which seriously limit its applications.Preparation of graphene-based composites is one of the most effective ways to solve this problem.On the other hand,electrochemical methods provide useful alternatives due to their simplicity,high sensitivity,good stability,low-cost instrumentation,and on-site monitoring,and it has been widely used in health care,food industry and environmental protection.A key role played in electrochemical detection should be the modified electrode materials,which determines the sensitivity and speed of response to a large extent.In the present work,GO was used as a precursor to preparation of graphene and graphene-based composites in consideration of its large surface area,unique space structure and easily be modified.The as prepared graphene and graphene-based composites have be used to construction of a series of drug electrochemical sensors.Specific content is as follows:?1?Electrochemically reduced graphene oxide?RGO?based voltammetric sensors have drawn considerable attentions due to their simple preparation process and outstanding electrochemical properties.While quite a lot of work suffers from problems in terms of sensitivity and cycling stability.Here,we demonstrate that the reduction extent of RGO displays a crucial role in enhancing sensitivity and preventing electrode fouling.To illustrate this,partially reduced and relatively complete reduced RGO films were prepared via electrochemical method.The reduction extent was controlled by performing cyclic voltammetry with varieties of reduction cycle numbers.Results indicated that partially reduced RGO film with 5 reduction cycle numbers?RGO₅?showed highest sensitivity towards electrochemical oxidation of isoniazid?INZ?among all the RGO films with different reduction extent.Under the optimal conditions,the peak currents on RGO₅ modified electrode increased linearly with the concentrations of INZ in the range of 0.09–100?M.The detection limit of INZ reached 15 nM?S/N=3?.The proposed method was successfully used for detecting INZ in human urine samples.?2?Reducedgrapheneoxide-multiwalledcarbonnanotubes?RGO-MWCNTs?composites were prepared by electrochemical method.The incorporated multiwalled carbon nanotubes?MWCNTs?served as electrical conducting wires,which could facilitate the electrochemical reduction of graphene oxide?GO?.Compared to either electrochemically reduced graphene oxide?RGO?or MWCNTs,integrating these nanostructures resulted in a strong synergistic effect between the two materials consequently leading to a superior hybrid material with higher activity for the electro-oxidation of DES.The electron transfer coefficient???,the standard rate constant?k_s?and electrochemically effective surface area?A?were calculated.Under the optimized conditions,RGO-MWCNTs modified electrode exhibited better linearity than either RGO or MWCNTs over ranges from 0.01 to 40?M with the detection limit of 3 nM?S/N=3?.The proposed method also exhibited good repeatability and long-term stability.?3?Sandwich-structured Pt-graphene-Pt?P-Gr-P?nanocomposite has been prepared by a facile two-step synthesis method.P-Graphene oxide-P?P-GO-P?nanocomposite was firstly synthesized by an in situ growth method,during which platinum nanoparticles?PtNPs?grew on both sides of GO.In the second step,P-GO-P was modified onto GCE and experienced an electrochemical process,GO in P-GO-P nanocomposite was reduced to a more conductive form of Gr.The obtained sandwich-structured P-Gr-P can effective separate the individual layers of Gr sheets,prevent the agglomeration between Gr sheets and improve the conductivity of the Gr film.In addition,the electrocatalytic properties of the as prepared P-Gr-P nanocomposite towards the oxidation of salbutamol were investigated.Results revealed that the sandwich-structured P-Gr-P nanocomposite with higher electrochemically active surface area showed better electrocatalytic activity toward salbutamol oxidation than PtNPs-Gr prepared by one-step electrochemical co-deposition method.Under the optimal conditions,the peak currents on P-Gr-P modified electrode increased linearly with the concentrations of salbutamol in the range of 0.03–180?M.The detection limit of salbutamol reached 9 nM?S/N=3?.The proposed method was also used for detecting salbutamol in human urine samples with satisfactory results.Three-dimensional graphene?3D GR?microspheres have been successfully prepared for the first time by a simple facile and green method using?-cyclodextrin aggregates??-CDAs?as substrates.The synthesized 3D GR/?-CDAs composites have been characterized by scanning electron microscopy?SEM?,transmission electron microscopy?TEM?and Raman spectroscopy.A possible formation mechanism was discussed.The as-prepared3D GR/?-CDAs microspheres provided multidimensional electron-transport pathways,and this has been exploited in an electrode material for the electrocatalytic oxidation of midecamycin.Electrochemical results indicated that the as-prepared 3D GR/?-CDAs microspheres exhibited a higher electrocatalytic activity towards midecamycin oxidation than 2D GR or?-CDAs.Under the optimalconditions,thepeakcurrentsona3DGR/?-CDAs microspheres-modified electrode increased linearly with the concentration of midecamycin in the range 0.07–250?M.The detection limit of midecamycin reached 20 nM?S/N=3?.Moreover,the proposed sensor also exhibited good repeatability,stability and anti-interference ability.